Finding any non-standard/default permission policy, fine-grained permission
checking will be enforced, intentionally removing the opt-out for safety.
Thanks to Odd Simon Simonsen for bringing-up the idea in the first place.

Parsing ticket fields per request has been a known performance hog, that's why
using the tags db table for regular access yields a considerable speed-up.

As a side-effect 'ticket' is the pilot for fixing a recently announced issue
with get_tagged_resources in the default tag provider implementation.
Nicely polished by stretching unit test coverage to this part of the code.

ToDo:DefaultTagProvider must be fixed as well, and other tag
providers should be reviewed too as a precaution.

fix of reported problem: While activating mastertickets compatibility adding ticket dependencies might cause problems. I.e., a conflict is shown by Trac while editing dependencies AND another field at the same time.

new option at admin panel worksaround the problem: enable_save_dependency_changes_to_ticket_comments

Removed one instance of the duplicated function date_range. macro.py now imports this function from ticketstats.py. get_num_closed_tix and get_num_open_tix are now non-member functions. Eventually, they will be shared between the macro.py and ticketstats.py modules.